Historically, garage doors evolved from barn doors. Thus, garage doors originally had either two door members which were hinged at the sides of the garage entry opening, or a single door member which could be spring or counterbalance lifted into the ceiling of the garage. As these designs were impractical for many applications, a sectional garage door was the next major innovation in the development of the garage doors.
A sectional door generally consists of a plurality of vertically superimposed panel sections, lace hardware, rollers and two parallel tracks. The panel sections extend the width of the garage entry opening and are typically between 12 to 24 inches in height. Vertically adjacent panel sections are united and controlled by the face hardware which consists primarily of hinges. Each of the two parallel tracks is positioned at a side of the garage entry opening. Rollers are attached to the sides of the panel sections which slide through the track permitting the sectional door to be moved between raised and lowered positions.
The original panel sections for sectional doors were manufactured of wood. From 1940 through 1965 wood sectional doors dominated the marketplace. There are two types of wood panel sections, those of a raised or recessed design and those of a flush design.
A panel section of a raised or recessed design wood door consists of top and bottom rails which are united by vertical members called styles to form a unitized frame. Shaped wood pieces fill the areas inside of the rails and styles to complete the panel section.
A panel section of a flush design wood door consists of a unitized frame made of rails and styles similar to the panel design. A flush sheet of wood or wood composite material is bonded to the front, or to both the front and back of the unitized frame. If wood sheets are mounted to both the front and back of the unitized frame, the center or core of the panel sections defined by the space therebetween, may optionally be filled for additional strength and/or insulation. If filled, either a corrugated honeycomb or expanded polystyrene typically is used as a filler material.
Both designs of wood sectional doors include disadvantages which are inherent to the properties associated with wood. For example, wood has the tendency to split, crack, splinter, rot and warp, because it is sensitive to temperature and humidity changes, water absorption and sunlight. Further, many users find that wood panel sections do not provide sufficient impact resistance, wind resistance or thermal insulation properties. Wood panel sections are also typically heavier than many other types of panel sections, creating more stress on the connecting hardware, making it more difficult to manually raise and lower the garage door, and costing more money to raise and lower the garage door by an electrical opener. Additionally, wood panel sections frequently require continuous painting or staining to maintain their desired appearance.
The next technological advancement was the advent of the steel sectional door. Steel sectional doors started to dramatically replace the wood market with near domination in the current marketplace.
A steel door panel section consists primarily of a single sheet member having a vertical portion and generally horizontal top and bottom portions. A panel section is manufactured by roll forming a sheet of pre-coated steel coil stock. The roll forming process bends the sheet to form the top and bottom portions of the section in order to achieve the proper interface between vertically adjacent panel sections. Raised panels are stamped into the vertical portion of the sheet to increase panel section stiffness, resist oil canning, and provide an aesthetically pleasing design.
A steel commercial door panel section generally consists of a heavier gauge steel and is manufactured by roll forming not only the top and bottom portions but also horizontal fibs. These ribs are used in lieu of the stamped panels to achieve stiffness and resistance to oil-canning. The roll formed ribs reduce the cost of the panel section by eliminating the stamping process.
Advancements to steel doors have been minimal and have been centered around increases in thermal effectiveness and additional panel section strength. In one advancement, a block of expanded polystyrene is dropped into a hollow back side of the panel section, which is defined by the area behind the vertical front portion and in between the top and bottom portions, to insulate the steel panel section. In another improved design, a rear steel skin is introduced to sandwich the block of polystyrene. In yet another improved steel panel section design, individual front and back steel skins are roll formed and a polyurethane foam is poured or injected therebetween. The polyurethane foam expands to structurally enhance and increase the thermal efficiency of the panel section. Additionally, there have been thermal efficiency improvements in the panel sections themselves, between vertically adjacent panel sections, and in seals around the door.
However, steel sectional doors have some disadvantages which are inherent to the properties associated with steel. For example, steel has the tendency to rust, erode and deteriorate because it is sensitive to humidity changes and water exposure. Steel panel sections are also susceptible to denting upon a relatively small force applied thereto. Steel panel sections tend to be heavier than some other types of panel sections creating more stress on the connecting hardware, making it more difficult to install and manually raise and lower the garage door, and costing more money to raise and lower the door by an electrical opener. Further, the insulation properties of even insulated steel panel sections may not be adequate for some applications. Additionally, steel panel sections usually require continuous painting due to its propensity for color fading and scratching.
In addition to the wood and steel sectional garage doors, specialty sectional garage doors have been introduced which make use of aluminum, plastic, and/or fiberglass.
A garage panel section utilizing an aluminum frame and a plurality of blow-molded polyethylene panels is disclosed in U.S. Pat. No. 3,980,123 to Vago. The aluminum frame consists of horizontal support rails and vertical styles spaced approximately 3-4 feet apart. The polyethylene panels are placed inside the aluminum frame and are sized to fit vertically between adjacent rails and fit horizontally between adjacent styles. The prior art also includes a similar garage door panel section design with an aluminum frame and polyethylene panels which are twin-sheet vacuum formed as opposed to blow-molded.
While this panel section design with an aluminum frame and polyethylene panel sectional door includes improvements over the steel and wood garage doors, there are still drawbacks in the design. First, the aluminum frames are subject to corrosion. Second, the panel sections may not be structurally strong or wind resistant enough for many applications. Third, the price of these sections may be too expensive for many purchasers due to the cost of the aluminum frame and the cost of assembling the sections. Fourth, its thermal insulation properties may not be adequate for some applications. Additionally, polyethylene has a chemical make-up which is less stable than some other plastics which increases the possibility of color fading.
Fiberglass sectional garage doors have also been introduced into the marketplace. Fiberglass panel sections are similar in design to the steel panel sections with the primary difference being the material of the skins. A major advantage associated with these panel sections is that fiberglass skins will not dent or rust like steel skins. However, fiberglass skins are susceptible to cracking from temperature changes and forces applied thereto. Further, foamed-in-place polyurethane cores which may be used in the fiberglass panel sections only mechanically bond with the fiberglass skins, and thus do not strengthen or control the thermal expansion properties of the fiberglass skins to the same degree as foam cores which chemically and mechanically bond to the skins.
A sectional garage door with panel sections having a corrugated steel rear skin strip and a polyvinylchloride front skin is disclosed in U.S. Pat. No. 4,339,487, to Mullet. Vertically oriented wood styles are inserted into steel rear strip to form flush ends for the sections. A vinyl film strip forms the front skin and includes a wetted polyurethane foam sprayed thereon. The vinyl film strip is applied over steel rear strip and the panel section is heated to expand the polyurethane foam. The expanded foam core serves the functions of a bonding agent and a thermal insulator. While this configuration improves upon the all-steel door designs, it still has many of the same problems associated therewith.
A sectional garage door made from steel reinforced, extruded polyvinylchloride panel sections has also been introduced by Skywood Extrusion Incorporated which is located in Canada. Each panel section includes two extruded polyvinylchloride elements which are fixedly joined together by a continuous roll-formed steel strut. Each extruded element includes a front skin surface and a rear skin surface which are joined together by top and bottom walls and two internal reinforcing fibs. The two internal reinforcing ribs provide important structural support for each extrusion and divide the space between the front and rear surfaces and the top and bottom walls into three vertically spaced internal sections. The three internal sections in each extrusion may be filled with polystyrene, isocyanurate foam, or foamed-in-place polyurethane as an insulator. Steel end caps are placed over each end section to provide structural support between the joined extrusions.
While this design utilizes some of the advantages associated with extruded polyvinylchloride, the design also includes disadvantages. First, the steel end caps and roll-formed steel struts which extend the width of the garage entry opening significantly increase the weight of the door and have disadvantages associated with steel doors, e.g., rusting and denting. Additionally, the two internal reinforcing ribs in each extrusion requires a larger quantity of polyvinylchloride which increases the cost of the panel sections. Further, the extrusions are not easily adaptable to provide an aesthetically pleasing look having raised or recessed panels.